Melting of polydisperse colloidal crystals in nonequilibrium

The influence of a time-dependent oscillatory external field on the melting transition of a polydisperse colloidal crystal is examined by theory and c omputer simulation. In a monodisperse crystal the field just induces an ove rall dynamical mode which does not affect the melting line. For a polydispe rse sample, on the other hand, the field shifts the melting line towards-sm aller temperatures. Combining a solid cell approach and a Lindemann criteri on in nonequilibrium, a simple theory is presented showing that the tempera ture shift scales with the square of the relative polydispersity. The theor y is in reasonable agreement with nonequilibrium Brownian dynamics computer simulations. [S1063-651X(99)11908-1].